The amount of sleep adults need has once again come under the spotlight, with a recent Wall Street Journal article suggesting seven hours sleep is better than eight hours and the American Academy of Sleep Medicine drawing up guidelines surrounding sleep need.

So, what should the guidelines say? Unfortunately, when it comes to the amount of sleep adults require there is not really a “one size fits all”. Sleep need can vary substantially between individuals.

Sleep is regulated by circadian and homeostatic processes, which interact to determine the timing and duration of sleep. The circadian process represents the change in sleep propensity over 24 hours, or our internal “body clock”. The homeostatic process represents the accumulation of sleep pressure during wakefulness and the dissipation of sleep pressure during sleep.

Both the circadian and homeostatic processes are influenced by internal factors, such as genes, and external factors, such as prior sleep history, exercise and illness. Individual variations in sleep timing and duration can be largely explained by these internal and external factors.

Individual sleep need

Genes are important in determining diurnal preference: whether we are “night owls” who prefer to stay up late at night, or “early birds” who prefer to get up early in the morning. Genes may also contribute to whether we are “short” or “long” sleepers.

But although genes form the foundation for sleep timing and duration, many external factors also affect sleep need.

Perhaps one of the more common causes affecting sleep duration relates to sleep history. Many adults, whether they know it or not, experience sleep restriction, often on a daily or weekly basis. Restricting sleep or going without sleep (pulling an “all-nighter”) increases sleep pressure.

Health, exercise, heavy labour, and even mental workload can affect sleep duration. During times of illness, following exercise, or even following periods of mental stress (such as exams), the amount of sleep needed to recover or restore back to normal can increase. Likewise, individuals who suffer from disease or who have poor health may need more sleep than their healthier counterparts.

Sleep need also varies with age, with elderly people generally sleeping less than younger individuals. Age-related changes associated with sleep duration are thought to be due to changes in the interaction between the circadian and homeostatic processes.

The individual variations in sleep need make it difficult to provide a specific recommendation as to how much sleep adults need. However, most sleep researchers generally agree that seven to nine sleep is what the majority of adults require to function at their best.

Why eight hours sleep?

Sleep restricted to seven hours or less results in impairments to reaction time, decision making, concentration, memory and mood, as well increased sleepiness and fatigue and some physiological functions.

On the other hand, eight hours or nine hours sleep has little impact, either negatively or positively, on performance.

Based on these findings, it would seem that for most of the adult population, somewhere between seven and nine hours of sleep is the “right amount”.

This is not to say that more than nine hours sleep is not good. Rather, extending sleep duration may help to “protect” waking function during subsequent periods of sleep loss. While we may not need ten hours sleep all the time, there are some clear benefits from getting more sleep.

But I am fine with six hours sleep…

The first question you need to ask yourself is, are you really?

You may be one of the lucky few with the “right” genetics. However, it’s more likely that you are simply unaware of how sleep loss is impairing your waking functions.

How we feel does not always reflect how badly we may be functioning, which may result in delusions about how much sleep we really need. Needing an alarm clock to wake up and the desire to sleep-in on weekends/holidays suggests that sleep need is not being met.

Critically though, if you have difficulty sleeping for a continuous eight hours, try not to worry too much, as this may make things worse.

Finding your optimal sleep duration

The amount of sleep need can vary significantly and can depend on multiple different factors, making it difficult to work out optimal sleep need. Below is a guide that might help to determine sleep need.

Keep a diary of your sleep. Include the times you went to bed and woke up, how you slept and how you felt during the daytime

Go to bed when you feel sleepy/tired

If you can, don’t use an alarm clock, rather, let your body naturally wake up

Try to get natural sunlight exposure during the day

Keep to a regular sleep schedule all days of the week.

After a while, you should be able to work out the best timing and duration for your sleep. If you are still unsure or concerned, see your general practitioner. Remember, though — sleep need can change with circumstances, so always listen to your body.